erlang元组转列表原理

erlang:tuple_to_list/1
的原理是什么？

http://www.tuicool.com/articles/n6fAr2B

/* convert a tuple to a list */

BIF_RETTYPE tuple_to_list_1(BIF_ALIST_1)
{
    Uint n;
    Eterm *tupleptr;
    Eterm list = NIL;
    Eterm* hp;

    // 判断是否是元组
    if (is_not_tuple(BIF_ARG_1))  {
    BIF_ERROR(BIF_P, BADARG);
    }

    // 获取头地址
    tupleptr = tuple_val(BIF_ARG_1);
    n = arityval(*tupleptr);
    // 申请列表内存空间
    hp = HAlloc(BIF_P, 2 * n);
    tupleptr++;

    // 循环拷贝
    while(n--) {
    list = CONS(hp, tupleptr[n], list);
    hp += 2;
    }
    BIF_RET(list);
}

/**********************************************************************/

/* convert a list to a tuple */

BIF_RETTYPE list_to_tuple_1(BIF_ALIST_1)
{
    Eterm list = BIF_ARG_1;
    Eterm* cons;
    Eterm res;
    Eterm* hp;
    Sint len;

    if ((len = erts_list_length(list)) < 0 || len > ERTS_MAX_TUPLE_SIZE) {
    BIF_ERROR(BIF_P, BADARG);
    }

    hp = HAlloc(BIF_P, len+1);
    res = make_tuple(hp);   // 和元组转列表的最大区别，添加了元组标识
    *hp++ = make_arityval(len);
    while(is_list(list)) {
    cons = list_val(list);
    *hp++ = CAR(cons);
    list = CDR(cons);
    }
    BIF_RET(res);
}